Semiconductor manufacturers need a practical and effective method of inspecting their dies. One system presently available to the manufacturers is a scanning electron microscope (SEM) voltage contrast (VC) system. Use of the SEM VC system to test a die, however, creates a surface charge problem on the die which interferes with testing.
Another voltage contrast system generates electrons from a metal surface by photo excitation. In such systems, testing must be performed in a vacuum. When a dielectric covers the metal, "low level," UV excitation is used to partially ionize the dielectric. This allows conduction of the photo generated electrons to the surface of the dielectric where they can be detected.
Currently, at least part of the die passivation must be removed for successful SEM VC system testing. Removal of all die passivation, however, poses the risk that the die will not function. A focused ion beam mill or a laser by ablation or chemical means can act to remove passivation from localized spots on the die. An application of photo resist can be used as an etch mask for spot removal of passivation. The resist is patterned where desired by scratching the resist or exposing the resist to light/SEM and subsequently developing the resist. An etch of the passivation then removes the material from the spot to be analyzed by the SEM VC system. Unfortunately, all of these techniques are slow and limited in the number of locations which can be easily processed.
What is needed is a method that prevents surface charge problems associated with SEM VC system testing of a die without the removal of die passivation. Also needed is a method of collecting the charge from passivated devices which are subject to photo excitation without the need for a vacuum chamber.